Method for the removal of excess penetrant and simultaneous development of color indications

ABSTRACT

A METHOD FOR THE REMOVAL OF EXCESS COLORED LIQUID PENETRANT AND THE SIMULTANEOUS DEVELOPMENT OF COLOR INDICATIONS, THEREBY ELIMINATING BOTH THE SEPARATE STEP OF FIRST REMOVING EXCESS PENETRANT BY EMULSIFICATION AND WATER WASHING, AND THE SEPARATE SUBSEQUENT STEP OF APPLYING A DEVELOPER. THE PRESENT METHOD EMPLOYES A PIGMENTED AQUEOUS REMOVER-DEVELOPER COMPOSITION CONTAINING A NONVOLAITLE SURFACTANT AND PREFERABLY A GLYCOL-TYPE OF DEGELLING AGENT. THE REMOVER ITSELF SERVES TO REMOVE THE EXCESS OF COLORED LIQUID PENETRANT FROM THE SURFACE OF THE WORKPIECE WITHOUT REMOVING ANY PENETRANT ENTRAPPED IN SURFACE DISCONTINUITIES, AND AT THE SAME TIME A PORTION OF THE COMPOSITION REMAINS AS A RESIDUAL SURFACE FILM OF THE SURFACTANTS AND PIGMENT TO DEVELOP THE COLOR INDICATIONS.

United States Patent U.S. Cl. 73104 8 Claims ABSTRACT OF THE DISCLOSURE A method for the removal of excess colored liquid penetrant and the simultaneous development of color indications, thereby eliminating both the separate step of first removing excess penetrant by emnlsification and water washing, and the separate subsequent step of applying a developer. The present method employs a pigmented aqueous remover-developer composition containing a n0I1- volatile surfactant and preferably a glycol-type of degelling agent. The remover itself serves to remove the excess of colored liquid penetrant from the surface of the workpiece Without removing any penetrant entrapped in surface discontinuities, and at the same time a portion of the composition remains as a residual surface film of the surfactant and pigment to develop the color indications.

SUMMARY OF THE INVENTION Themethod of my invention relates to an improvement in the penetrant method of inspecting workpieces for surface discontinuities. As generally practiced, the penetrant method includes (1) applying to the surface of' a workpiece a colored liquid penetrant, the liquid vehicle of which may be a water-immiscible liquid hydrocarbon; (2) allowing time for the penetrant to penetrate any surface flaws; (3) removing the excess of liquid penetrant on the surface, as by emulsification followed by or simultaneous with water washing; and subsequently, either with or without drying the surface, (4) developing any color indication at the locus of a surface flaw by the application of a wet or dry developer.

In accordance with my improvement steps (3) and (4') are eliminated as separate steps and are combined as a single step of simultaneously removing the excess of penetrant remaining on the penetrated surface and of applying a developer composition. This is accomplished by the use of a combined remover-developer in the form of an aqueous surfactant solution containing a suspended finely divided white, or light-colored pigment. The surfactant component, which is assisted preferably by a de-gelling agent, serves to remove the excess residual penetrant, and also to assist the pigment particles in functioning as the developer after the removal of the water, as by evaporation or drying.

Where the penetrant vehicle is water-immiscible, as is preferable, the surfactant in the remover-developer composition aids in the removal of the penetrant without removing entrapped penetrant by an agitated dip, spray or other turbulent method of application that involves considerable relative movement between the penetrated surface and the liquid remover-developer composition. Then, after the excess of remover-developer composition has been removed from the surface, as by draining, the residual remover-developer composition is dried, or allowed to dry in the atmosphere. The pigment particles as they dry, assisted by the surfactant, serve to develop the color indication by absorbing the colored penetrant from the surface flaws as the same is drawn out by capil- 3,554,020 Patented Jan. 12, 1971 lary and other forces of attraction to the pigment particles. If a fluorescent color was used in the penetrant, the resulting color indication is viewed under black light, or if a visible color was used, the observation is made under white light. Post removal of the remover-developer is accomplished by washing oil with water, assisted by the residual surfactant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid portion of the remover-developer composition of my invention preferably comprises in its concentrated form the following:

EXAMPLE ILIQUID CONCENTRATE Ingredients: Percent by weight Surfactant (non-volatile) 10-100 Glycol-type de-gelling agent -0 Water Balance Since it is not feasible to add the required amount of pigment to the liquid concentrate, due to excessive thickening, the concentrate is first diluted with water to an extent such that the liquid concentrate constitutes from 0.2 to 10% of the resulting solution by weight, and the pigment is then dispersed ,in the diluted concentrate until the proper proportions of liquid concentrate and pigment are obtained.

Alternatively, the remover-developer composition can be supplied in the form of a cake containing all of the necessary ingredients which, when dispersed in a proper volume of water, will result in a ready-to-use spray-type remover-developer. For example, if a 0.5% concentration is desired, 50 lbs. of pigment can be mixed with one-half /2) gals. of the foregoing liquid concentrate to form a substantially dry cake, and the cake dispersed into gals. of water with mechanical agitation to form the readyto-spray remover-developer dispersion. By changing the amount of water, the concentration of both the remover and developer can be regulated within the above limits of 0.2 to 10% non-aqueous content by weight.

The composition of the final remover-developer will depend upon whether it is to be used on a recirculative or on an expendable basis for the removal of the excess penetrant. If on a recirculative basis the ultimate formula will be as indicated:

EXAMPLE II.RECIRCULATIVE Percent by weight As surfactant any of the following can be used, separately or in admixture, within the ranges of percentages by weight given above:

(1) Nonionic, normally liquid alkylphenoxy polyethoxylated ethanols, wherein the alkyl radical contains from 8 to 10 C-atoms, preferably octyl or nonyl; and which contain a sufficient number of ethylene oxide groups (ETO), between 5 and 15 ethylene oxide groups per mol, to render the surfactant Water soluble, or at least water miscible, and completely miscible with the glycol-type of de-gelling agent;

(2) Nonionic, normally liquid ethoxy fatty alcohols, including polyethoxylated straight chain primary C C alcohols containing from 6.5 to 15.5 ethylene oxide groups per mol of alcohol;

(3) Fatty acid esters of polyglycol thers, such as alkoxypolyoxyethylene ethanols that are availab e as nonionic liquid detergents;

(4) High molecular weight fatty acid amides, such as a lauric alkanolamide and mixed fatty acid amides;

(5) Acetylenic glycols and their ethoxylated derivatives such as acetylenic glycol 2, 4, 7, 9 tetramethyl, and a mixture of the tetramethyl decynediol and an alkyl phenyl ether of polyethylene glycol in ethylene glycol;

(6) Ethoxylated fatty acid esters of sorbitan; and

(7) Organo silicone surfactants, believed to be the reaction product of an organic silicone (siloxane) and a nonionic wetting agent.

Nonionic surfactants are preferred, but anionic surfactants can be used also. Cationic surfactants are not satisfactory for use where the pigments are clays, since the cationic surfactants tend to cause coagulation of the clay suspension.

De-gelling agents that have been found suitable for my purposes are the following:

Ethylene glycol; butyl Cellosolve (ethylene glycol monobutyl ether), and other water-miscible glycols, glycol ethers and glycol esters, all of which are herein referred to as glycol-type de-gelling agents.

Pigments suitable for use include clays such as bentonite, Buca and other natural and proprietary clays, natural and proprietary pigments, such as Titanox, a titanium dioxide; Alon C, which is an aluminum oxide (A1 magnesium oxide (MgO) and talc; and especially prepared silicas such as Microcel-C, Santocel and Cab-O-Sil (a pyrogenic silica). These are all white or light colored pigments, suitable for use as developers. Of all of them, bentonite and Alon C, either separately or in admixture, proved most satisfactory as pigment type developers.

In general, the concentration of pigment used in the remover-developer composition, whether of the higher content of from to 10% liquid concentrate for use on a recirculative basis, or of the lower content of from 0.1 to 2% for use on an expendable basis, should be between the limits of about /s% and 3% or even 5% by weight pigment of the total remover-developer composition. The concentration of the developer pigments determines the thickness of the coating. This, in turn, affects the behavior of the penetrant after drying. With large defects, a thin coating causes excessive bleeding of the penetrant, whereas a thick coating serves to control such bleeding more satisfactorily. On the other hand, low concentrations of pigments provide thin coatings that serve to indicate very fine defects that thick coatings would mask. For maximum enhancement of the fluorescent brightness of the color indications during their development, the concentration should be chosen that gives the best possible results.

The particle size range of the pigment particles should be maintained between varying limits depending upon the magnitude of dimensions of the surface defects that are to be detected, but be generally between 1 micron or less and not over about 5 or 7 microns as the maximum particle size dimension. Alon C, which is a fluffy, very fine aluminum oxide, works excellently alone, but is relatively expensive so is usually extended by mixing a clay therewith. Alon C aids in re-dispersing clays or other pigments that settle out on standing. Bentonit, despite its tendency to swell in contact with water, can be used quite satisfactorily, but not in total amounts greater than about 3% by weight of the total removerdevelop composition, in whatever dilution it is used.

Where the penetrant system is carried out in steel or iron equipment, the usual rust inhibitors, such as sodium nitrite and sodium chromate are employed. Also, waxy substances that aid in causing the pigments to adhere in finely divided, discrete form to the test surface can be included in the remover-developer composition.

The following is an example of an inhibited aqueous suspension containing a film-forming waxy substance:

EXAMPLE IV Surfactant: lbs. Ethoxylated (l2 ethoxy) nonyl phenol 15 Pigments:

Calcium carbonate 250 Volclay 625 200 Total 450 Inhibitor:

Sodium nitrite 15 Sodium chromate 4 Total 19 Carbowax 450 Water, to 10,000 lbs.

In Example IV, the Carbowax 4000, which is a proprietary synthetic, water-soluble wax having a water solubility of about 100 grams in 100 cc. of water at 20 C., serves as a film-former to aid in causing the finely divided pigment particles to form a more or less uniform but discrete particle deposit on the surface of the workpiece. It assists in the post development removal of the pigment particles and the non-volatile residue of the surfactant from the surfaces by a water-washing step. It does not aid in the developing action itself, but does aid, in connection with the Wetting agent, or surfactant, in achieving good wetting and spreading characteristics.

In place of Carbowax 4000 other members of this series of waxes which are believed to be polyethylene glycols, and which are hard or medium hard waxes, can be used so long as they are water soluble, non-volatile and are preferably solid at room temperature and have viscosities of at least about 100, Saybolt, secs. at 210 F. Other water-soluble film-formers can be used within the broad range of from 0 to 10% of the total remover-developer composition, such as: hydroxymethyl cellulose (Methocel H 6); sodium carboxymethyl cellulose (CMC); and acacia, or gum arabic and other natural and synthetic water soluble gums.

My remover-developer composition is itself free from any appreciable amount of dye, whether fluorescent or visible, so as not to interfere with the development of color indications, and is also free from sulfur-and/or phosphorus-containing compounds where avoidance of such compounds is necessary in order to inhibit embrittlement of high nickel-containing metal surfaces. Clays free of sulfur and chlorine are therefore preferred. White, cream-colored or light-cream-colored clays having a brightness of around or higher on a General Electric refiectometer are most suitable.

As previously stated, my improvement is particularly adapted for use where the penetrant liquid vehicle is substantially 'wholly water-immiscible, as in the case of penetrants used in the post-emulsification method, but water-washable penetrants can be used.

The post removal of the developer pigments is controlled by the concentration of the remover portion, namely, the aqueous surfactant portion of the remover-developer composition. The higher the concentration of the surfactant, the easier it is to remove the developer particles from the surface by water washing after the development of the color indications.

I claim as my invention:

1. In a method for detecting surface discontinuities in a workpiece by the application to said surface of a waterimmiscible colored penetrant liquid, the improvement that avoids separate penetrant removal and development steps, which comprises:

applying to the penetrated surface without prior removal of the penetrant remaining on said surface an aqueous solution of a surfactant containing pigment particles suspended therein, and drying said surface. 2. In a method for detecting surface discontinuities in a workpiece that includes applying to said surface a colored penetrant liquid to efiect penetration of said liquid into such surface discontinuities and entrapment therein, the improvement which comprises:

without prior removal of excess penetrant liquid remaining on said surface, applying to said penetranttreated surface a dilute aqueous remover-developer composition containing a surfactant dissolved therein and finely divided pigment particles dispersed therein, and effecting a substantial removal of said remover solution while leaving pigment particles on said surface to function as a developer of color indications generated by an interaction between entrapped penetrant and said pigment particles, whereby a separate development step is eliminated. 3. The method as defined by claim 2, wherein said penetrant liquid is colored by a fluorescent dye and is itself immiscible with water, and said surface is dried after effecting a substantial removal of said remover-developer composition. 4. The method as defined (by claim 3, wherein said remover-developer composition contains from about 0.1 to 7.5% by weight of a non-volatile surfactant and from 0.1 to by weight of pigment,

and said remover is applied with sufiicient relative movement between the solution and the penetrant treated surface to remove the excess penetrant on said surface without removing the entrapped penetrant.

5. The method as defined by claim 2, wherein said aqueous remover-developer composition contains a glycol-type de-gelling agent.

6. The method as defined by claim 5, wherein said aqueous remover-developer composition contains a water-soluble film-former.

7. The method as defined by claim 6, wherein said remover-developer composition contains from 0.1 to 7.5 of a non-volatile surfactant, from 0 to 9% of a glycol-type de-gelling agent, from 0.1 to 5% of a finely divided, light-colored pigment, and from 0 to 10% of a water-soluble film-former.

8. The method as defined by claim 7, wherein said remover-developer composition contains from 0.1 to 2% of a non-volatile surfactant, from 0 to 2% of a glycol-type de gelling agent, from 0.15 to 3% of a finely divided light-colored pigment and from 0 to 10% of a water-soluble film-former.

References Cited UNITED STATES PATENTS 3,114,039 12/1963 SWitzer 2507l 3,184,596 5/196'5 Alburger 250 71 3,349,041 10/1967 Alburger 25230'l.2

RICHARD C. QUEISSER, Primary Examiner E. J. KOCH, Assistant Examiner US. Cl. X.R. 

